Chao Gao 26f827e095 dma-direct: avoid redundant memory sync for swiotlb ... commit 9e02977bfad006af328add9434c8bffa40e053bb upstream. When we looked into FIO performance with swiotlb enabled in VM, we found swiotlb_bounce() is always called one more time than expected for each DMA read request. It turns out that the bounce buffer is copied to original DMA buffer twice after the completion of a DMA request (one is done by in dma_direct_sync_single_for_cpu(), the other by swiotlb_tbl_unmap_single()). But the content in bounce buffer actually doesn't change between the two rounds of copy. So, one round of copy is redundant. Pass DMA_ATTR_SKIP_CPU_SYNC flag to swiotlb_tbl_unmap_single() to skip the memory copy in it. This fix increases FIO 64KB sequential read throughput in a guest with swiotlb=force by 5.6%. Fixes: 55897af630 ("dma-direct: merge swiotlb_dma_ops into the dma_direct code") Reported-by: Wang Zhaoyang1 <zhaoyang1.wang@intel.com> Reported-by: Gao Liang <liang.gao@intel.com> Signed-off-by: Chao Gao <chao.gao@intel.com> Reviewed-by: Kevin Tian <kevin.tian@intel.com> Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>		2022-04-20 09:23:30 +02:00
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coherent.c
contiguous.c
debug.c	dma-debug: fix return value of __setup handlers	2022-04-08 14:40:25 +02:00
debug.h
direct.c
direct.h	dma-direct: avoid redundant memory sync for swiotlb	2022-04-20 09:23:30 +02:00
dummy.c
Kconfig
Makefile
mapping.c
ops_helpers.c	dma-mapping: handle vmalloc addresses in dma_common_{mmap,get_sgtable}	2021-07-28 14:35:38 +02:00
pool.c	dma/pool: create dma atomic pool only if dma zone has managed pages	2022-01-27 10:53:44 +01:00
remap.c
swiotlb.c	swiotlb: fix info leak with DMA_FROM_DEVICE	2022-04-08 14:39:46 +02:00
virt.c